The present invention relates generally to systems and methods for the evaluation of a circulatory function and, more particularly, to systems and methods for analyzing propagation of blood stream attributes through a circulatory system to identify an attribute thereof and, thereby, acquire clinically useful information about a subject.
In an individual, a large number of conditions can result in poor operation of and blood flow through the circulatory system. Example conditions include, but are not limited to, vessel occlusion, loss of muscular tone, edema, arterial hardening, peripheral arterial disease, artherosclerosis, abnormal sympathetic or parasympathetic function, and cerebral or autonomic dysfunction.
In many cases, to diagnose these conditions by the analysis of blood flow through an individual, it is necessary to use expensive imaging equipment to detect and/or quantify an ineffective operation of the circulatory system, or highly trained personnel, or both. For example, imaging devices such magnetic resonance imaging (MRI) systems can be used, such as to perform so-called functional MRI (fMRI) procedures that rely on the as blood-oxygen-level-dependent (BOLD) contrast mechanism, to acquire indirect information about the flow of blood through a subject. As another example, an MRI system can be used in conjunction with an injected contrast agent that flows through and can be imaged within the vasculature to identify abnormal attributes of blood flow through an individual's circulatory system. Using these images, clinicians attempt to trace the abnormal attributes to a particular condition. Unfortunately, these imaging systems are expensive and complicated to operate making the diagnosis of a condition by these methods expensive and time consuming. Furthermore, in the case of so-called contrast enhanced MRI studies that rely on the injection of a gadolinium-based contrast agent, there are clinical indications and scientific evidence that the contrast agent, itself, can be extremely harmful to a sub-section of the population and, in the case of nephrogenic systemic fibrosis, deadly. Other methods include the use of injected radioactive tracer materials, which carry their own risks and expense. Other methods, such as ankle brachial index (ABI) measurements, require trained operators, and manipulations of blood flow with pressure cuffs which may be difficult or impossible in some patient groups, such as the obese.
These existing methods also are measurements at a single point of time, and in most cases require moving the subject to a procedure room. These methods cannot be used for continuous circulatory monitoring, or monitoring at home, for example.
Therefore, it would be desirable to have alternative or even complementary systems and methods for evaluating the performance of a subject's circulatory system, particularly, systems and methods that are more widely available and more cost effective than expensive imaging modalities, such as MRI and radionuclide methods, and is free of associated health risks, and systems that can measure circulation passively, continuously, and/or automatically.